1. Field of the Invention
The present invention relates to an image forming apparatus, an image formation control method, and a computer program product.
2. Description of the Related Art
With an electrophotographic image forming apparatus, an electrostatic latent image is formed on a photoconductor on the basis of image data, and the electrostatic latent image is developed with a recording agent such as toner so that a recording agent image (hereinafter referred to as a toner image where appropriate) such as a toner image is formed. The image forming apparatus transfers the toner image on the photoconductor onto a recording medium (hereinafter simply referred to as a “sheet”) such as a sheet or a film conveyed between the photoconductor and a transfer roller, and conveys the sheet on which the toner image is transferred to a fixing unit.
The fixing unit typically includes a fixing roller having a fixing heater therein and being configured to be heated to a fixing temperature by the fixing heater and driven to rotate, and a pressure roller that is pressed by the fixing roller and rotates therewith. When a sheet on which a toner image is transferred is conveyed to the fixing unit, the fixing unit heats the sheet while holding and conveying the sheet between the fixing roller and the pressure roller to fix the toner image on the sheet to the sheet.
The image forming apparatus of the related art then starts feeding power to the fixing heater of the fixing unit to raise temperature at the same time as starting a process of forming an electrostatic latent image on the photoconductor, that is, starting image forming operation, and heats the fixing roller to a fixing temperature suitable for fixing a toner image onto a sheet before the sheet is conveyed to between the fixing roller and the pressure roller.
In the meantime, while there also have recently been demands for reducing power consumption of image forming apparatuses, power consumption of the fixing unit, that is, consumption of fixing power is large in an electrophotographic image forming apparatus. There are thus demands for saving fixing power in image forming apparatuses.
Note that, in an image forming apparatus, the temperature of the fixing roller needs to be raised to such a temperature that does not cause fixing failure even when the voltage of an external commercial power supply to the image forming apparatus is a lower voltage limit according to a standard. Thus, in an image forming apparatus of the related art, feeding of the power to a fixing heater is started at a timing at which a fixing roller can be heated to a fixing temperature before a sheet reaches the fixing roller even when the voltage of an external commercial power supply is a lower voltage limit. When the external commercial power supply has a normal power supply voltage higher than the lower voltage limit, power feeding control to maintain the fixing roller at the fixing temperature therefore needs to be performed on the fixing heater from when the fixing roller is heated to the fixing temperature before the sheet comes into contact with the fixing roller until when the sheet then comes into contact with the fixing roller. As a result, power is wasted after the fixing temperature is reached until the fixing operation is actually carried out.
In the related art, there is proposed an image forming apparatus including a main power supply, an auxiliary power supply including a chargeable and dischargeable power storage device, and a fixing device including a heating element that produces heat when power is supplied from at least one of the main power supply and the auxiliary power supply, wherein when a voltage value input from a commercial power supply to the main power supply, environmental temperature, or the voltage value of the auxiliary power supply is not larger than a predetermined value, power stored in the auxiliary power supply is not supplied to the fixing device at start-up (refer to Japanese Laid-open Patent Publication No. 2008-311240).
Thus, in this related art, power consumption of the auxiliary power supply is suppressed by suppressing power supply from the auxiliary power supply.
In the related art taught by the aforementioned publication, however, since only supply of auxiliary power is suppressed, power consumption from when the fixing temperature is reached until when actual fixing operation is carried out cannot be reduced, and improvement is required for reducing power consumption for fixing.
In view of the above, there is a need to reduce power used for fixing.